WASHINGTON — First launched nearly 20 years ago, the International Space Station has served as an orbiting laboratory, an observation platform and a gleaming testament to international cooperation.

But in a time of limited budgets and grander ambitions, there are key questions about the future of the aging outpost that spans the length of a football field:

How much longer is the U.S. willing to spend $3 billion to $4 billion annually to maintain operations?

Will other partners step in?

Is it approaching the end of its usefulness?

There’s no immediate rush for answers since Congress two years ago extended space station operations until 2024. But the clock is ticking: The NASA Transition Authorization Act that President Donald Trump signed Tuesday requires the agency to begin charting the space station’s future beyond 2024.

Count Rep. Brian Babin, R-Texas, chairman of a House Science, Space and Technology subcommittee, among those who think NASA’s long-term sponsorship of the space station could hamper the nation’s ultimate goal of sending astronauts to Mars.

“We ought to be aware that remaining on the ISS will come at a cost (beyond 2024),” Babin said during a hearing Wednesday. “That cost means trade-offs with other NASA priorities.

"What opportunities will we miss if we maintain the status quo? ... The longer we operate the ISS, the longer it will take to get to Mars.”

Babin referred to a NASA Inspector General report in 2014 that projects rising maintenance costs.

Those projected costs include the risk of insufficient power generation, due in part to faster-than-expected degradation of its solar arrays and the difficulty of transporting large replacement parts to the station.

Talk of abandoning, or even handing over, operations of the space station to another entity might sound like Space Age heresy, given the myriad achievements over two decades.

Those achievements have included vaccine development, water purification advances, three-D printer technology and the study of how living in space affects humans. The latter research is considered crucial for planning a months-long mission to Mars.

In addition, the station has been an important incubator for the commercial space industry, which now transports cargo — and could start ferrying astronauts next year — to the space station.

Keeping the station operational is “critical” to the continued maturity of the commercial space industry, said Eric Stallmer, president of the Commercial Spaceflight Federation, which advocates extending the U.S. commitment through at least 2028.

“We would lose our outpost in space,” Stallmer told lawmakers.

William Gerstenmaier, associate NASA administrator for human exploration and operations, said it’s unlikely the agency would recommend moving on from the space station any time soon, given the important discoveries it continues to find as a lab for the deep-space missions to follow.

The damaging effect that long-term exposure in low Earth orbit has on human vision, for example, was a fairly recent discovery, he said.

But he also said NASA’s predominant role eventually should be a focus on deep space that includes a “smooth hand-off” from the current situation.

The $67 billion space station, which weighs 925,000 pounds, took 12 years to build.

And it served as a beacon of international cooperation with its five landlords: the U.S., Russia, Japan, Canada and Europe.

Rep. Dana Rohrbacher, R-Calif, recalled how he voted for the program even as some in Congress were skeptical.

“There were many promises that cancer would be cured. While I never did buy that, I hoped it would be true,” he said Wednesday. “But I do think we can say that when we write the history of what was accomplished the last century, the space station will be on the list.”